1. Field of the Invention
The present invention relates to a semiconductor device and more particularly, to a plastic-molded semiconductor device with a semiconductor pellet or pellets mounted on a lead frame.
2. Description of the Prior Art
A conventional semiconductor device of this type is shown in FIG. 1A. A semiconductor pellet or die 103 is mounted on a die pad 102 of a leadframe 101, and bonding wire pieces 104 are bonded at their ends to interconnect bonding pads or electrodes of the die 103 and corresponding inner leads 101a of the leadframe 101.
The semiconductor pellet 103, the bonding wire pieces 104 and the inner leads 101a are molded in a plastic package 105. Outer leads 101b of the leadframe 101 protrude from the package 105 to the outside thereof.
To keep up with the progress in large-scale integrated circuits, another conventional semiconductor device of this type as shown in FIG. 1B has been developed, which is disclosed, for example, in the Japanese Non-Examined Patent Publication No. 60-160135.
With the prior art device shown in my FIGS. 1A and 1B a semiconductor wiring substrate 203 made of silicon or the like is mounted on a die pad 202 of a leadframe 201. A patterned wiring metal film, such as aluminum (Al), is formed on the surface of the substrate 203. A semiconductor pellet 204 is bonded on the metal film to be mounted on the wiring substrate 203.
Bonding wire pieces 205a are bonded at their ends to interconnect bonding pads or electrodes (not shown) of the die 204 to the wiring metal film of the substrate 203 with each other. Bonding wires pieces 205b are bonded at their ends to interconnect the wiring metal film and inner leads 201a of the leadframe 201.
The pellet 204, the substrate 203 with the wiring metal film, the bonding wire pieces 205a and 205b, and the inner leads 201a are molded in a plastic package 206. Outer leads 201b of the leadframe 201 protrude from the package 205 to the outside thereof.
With the above-described conventional prior art semiconductor device shown in FIG. 1A, the semiconductor pellet 103 and the inner leads 101a are electrically connected with each other by using the bonding wire pieces 104. Also, with the above conventional semiconductor device shown in FIG. 1B, the semiconductor pellet 204 and the wiring substrate 203 are electrically connected with each other by using the bonding wire pieces 205a; then, the wiring substrate 203 and the inner leads 205a are electrically connected with each other using the bonding wire pieces 205b.
Therefore, it is difficult to be reduce the distance between the adjacent bonding pads, or the bonding pad pitch, to 100 to 120 .mu.m or less which is the limit of wire bonding machines. As a result, there is a problem that when a large number of the bonding pads are provided for a larger scale integration of circuits. It is impossible or very difficult to be reduced in size according to the integration scale. This means that the plastic-molded semiconductor device cannot be down-sized.
Taking such the problem into consideration, an improved prior art structure of the semiconductor device is shown in FIG. 1C, in which electrical interconnections between a semiconductor pellet and inner leads are carried out without a wire bonding process.
In FIG. 1C, a leadframe 301 has a die pad 302 depressed below inner leads 301a thereof, and a semiconductor pellet 303 is mounted on the die pad 302. A tape piece 304 for Tape Automated Bonding (TAB) is placed on the pellet 303 and the inner leads 301a so that the bonding pads (not shown) of the pellet 303 and the inner leads 301a are electrically connected with each other through the tape piece 304.
The semiconductor pellet 303, the tape piece 304 and the inner leads 301a are molded in a plastic package 305. Outer leads 301b of the leadframe 301 protrude from the package 305 to the outside thereof.
Since the tape piece 304 for the TAB is made of an insulation film such as polyimide and is finely patterned conductors are formed on a surface of the insulation film. The conductors can be produced in a highly precise manner so that the pitch or distance of the conductors are in accordance with the bonding pads of the pellet 303.
In addition, the electrical interconnection between the patterned conductors of the tape piece 304 and the inner leads 301a can be obtained by positioning and directly bonding the tape piece 304 on the inner leads 301a and the pellet 303.
In a practical bonding process, the bonding pads of the pellet 303 are bonded to one end portions of the patterned conductors. Then, the semiconductor pellet 303 is mounted on the die pad 302. Subsequently, the other end portions of the conductors are bonded to the inner leads 301a.
With the conventional semiconductor device shown in FIG. 1C using the TAB tape piece 304, a step of positioning the tape piece 304 on the pellet 303 is required. Thereafter a step of mounting the pellet 303 with the bonded tape piece 304 to the die pad 302 is also required at the same time as the positioning of the tape piece 304 on the inner leads 301a. Therefore, there is a problem that the assembly process sequence is complicated.
Additionally, since the tape piece 304 extends along the contour of the pellet 303 to link the pellet 303 with the inner leads 301a, it is difficult for a molding material or resin is difficult to flow into a gap formed between the tape piece 304 and the die pad 302 during the molding process. As a result, there is another problem because a good property or quality of the package 304 is difficult to obtain.
Especially, when the die pad 302 is a size which is larger than the size of the pellet 303, the TAB tape piece 304 the size corresponding to the die pad 302, so that the molding material becomes more difficult to flow into the circumferential area of the pellet 303.
To avoid the latter problem, for example, the die pad 302 may be substantially the same size as the pellet 303. However, there arises a problem that standardization of parts or elements is impeded because the lead frame 301 has to be designed and produced according to every size of the pellet 303.